1. Field of the Invention
This invention pertains to the field of protein hydrolysates. More particularly, it relates to methods for controlling the viscosity of protein hydrolysates by adjusting their magnesium and calcium content.
2. Description of Related Art
Protein hydrolysates and the methods for their preparation are well known. Protein hydrolysates are commonly used in the food industry as flavor enhancers and are sources of "meat-like" flavor. In addition, they also are used for nutritional purposes, such as a protein supplement, as an amino acid source for infant formulas, in special dietary preparations and for parenteral administration of amino acids. Protein hydrolysates have also been found useful in cosmetics and health care products.
In general, protein hydrolysates are prepared by subjecting protein sources to chemical or enzymatic hydrolysis to form a mixture of amino acids or amino acids and peptides.
Chemical hydrolysis includes treatment of the protein source with either an acid or an alkali. Acid hydrolysis of the protein source results in the more physiologically acceptable "L-" form of the amino acids as compared to the less desirable "D-" form which is produced by alkali hydrolysis and which is rarely metabolized by the human body.
The protein sources are readily available from a variety of materials, including both animal and/or vegetable proteins. Animal protein hydrolysates may be obtained from essentially any meat source such as beef, pork, lamb, fowl, fish, etc. They may also be of lactic origin, e.g., casein, lactalbumin, etc. Vegetable protein hydrolysates may be obtained, for example, from wheat germ, rice bran, corn gluten, soy protein, linseed protein, peanut press cake, yeast, and the like. The protein content in these respective starting raw materials may vary from approximately 20 to 90% by weight.
In a typical acid hydrolysis process, for example, the protein source is contacted with hydrochloric acid to cause hydrolysis of the protein. After digestion is substantially complete, the aqueous slurry medium is neutralized with an alkali, such as sodium hydroxide, to stop the hydrolysis reaction, treated with activated carbon and then filtered to remove any insoluble protein and humin (undigested, insoluble material such as fibers) formed in the reaction. The resulting aqueous solution (whether formed as a result of chemical or enzymatic hydrolysis) may then be evaporated to produce three types of commercially available products: (1) a liquid containing about 40% solids by weight; (2) a paste containing about 85% solids by weight; or (3) an essentially dry powder.
A major problem that is encountered when using protein hydrolysates, however, is that upon storage, the viscosity generally increases with time. This is particularly evident and pronounced with those hydrolysates having a higher solids content, such as the commercially available paste. The viscosity of the paste can reach such high levels that it actually becomes rock-like in nature after prolonged storage. This presents difficulties in removing the paste from the container in which it is kept, even after heating. Once removed, it is also troublesome to then disperse and solubilize the paste as needed.